concept use case diagram in category blockchain

This is an excerpt from Manning's book Blockchain in Action. Login to get full access to this book.

The use case diagram for the vending machine coin counter and drink dispenser is shown in figure A.2. It has four use cases at the first level—insert coins, see drinks, select drink, and pick up drink—which are all direct stimuli or operations invoked by the customer. The insert coins operation in turn invokes the count coins use case, see drinks requires display drinks, and select drink results in deliver drink. These secondary use cases are not directly invoked or used by the customer. An important note is that a use case diagram is not like a traditional flow chart. It simply lists the operations in the elliptical use case symbols. The operational flow is not defined here.

Figure A.2 Use case diagram for vending machine

Try using draw.io, Microsoft Visio, or another tool of your choice to create the use case diagram and get some practice. The diagram in figure A.2 has been created using draw.io.

// modifiers
   modifier validPhase(Phase reqPhase)                             #1
    { require(state == reqPhase); 
      _; 
    } 
    modifier onlyChair()                                           #1
     {require(msg.sender == chairperson);
      _;
     }
 
    constructor (uint numProposals) public  {
        chairperson = msg.sender;
        voters[chairperson].weight = 2; // weight 2 for testing purposes
        for (uint prop = 0; prop < numProposals; prop ++)
            proposals.push(Proposal(0));        
        state = Phase.Regs;
    }
    
     function changeState(Phase x) onlyChair public {              #2
        
        require (x > state );                                      #3
        state = x;
     }
    
    function register(address voter) public validPhase(Phase.Regs)      
                                                   onlyChair {     #4
       
        require (! voters[voter].voted);                           #3
        
        voters[voter].weight = 1;
       // voters[voter].voted = false;
    }
 
   
    function vote(uint toProposal) public validPhase(Phase.Vote)  {
      
        Voter memory sender = voters[msg.sender];                  #5
        
        require (!sender.voted);                                   #6
        require (toProposal < proposals.length);                   #6
        
        sender.voted = true;
        sender.vote = toProposal;   
        proposals[toProposal].voteCount += sender.weight;
    }
 
    function reqWinner() public validPhase(Phase.Done) view 
                            returns (uint winningProposal) 
    {
       
        uint winningVoteCount = 0;
        for (uint prop = 0; prop < proposals.length; prop++) 
            if (proposals[prop].voteCount > winningVoteCount) {
                winningVoteCount = proposals[prop].voteCount;
                winningProposal = prop;
            } 
       assert(winningVoteCount>=3);                                #7
    }
}

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In section 9.2, you’ll explore an ERC721-compliant token representing real estate assets.